Eudendrium macquariensis, Watson, 2003

Watson, Jeanette W., 2003, Deep-water hydroids (Hydrozoa: Leptolida) from Macquarie Island, Memoirs of Museum Victoria 60 (2), pp. 151-180 : 154

Eudendrium macquariensis sp. nov.

Figures 3E–G

Material examined. Stn 44, NMV F91309 , holotype, abundant infertile colonies on stems and branches of other species of Eudendrium , specimen alcohol-preserved .

Description (of holotype). Stolons creeping over stems and branches of hydroid host, stems numerous, to 7 mm long; stems (pedicels) and stolons morphologically identical and 0.1 mm diameter. Stems monosiphonic, unbranched, straggling, straight or flexed, perisarc of stolons and pedicels distinctly to weakly rugose throughout. Hydranths very small, distal on pedicel, hypostome prominent, dome-shaped, surrounded by 10–14 tentacles. Perisarc of stolon and stems firm and of same thickness throughout.

Nematocysts of two kinds present, both undischarged: (i) small droplet-shaped euryteles, capsule 9–10 X 4–5 µm, very abundant in tentacles; (ii) bean-shaped capsule 9 X 4 µm, rare, site unknown.

Colour. Stolons white, stems clear pale yellowish, hydranths white.

Etymology. The specific name refers to the type locality.

Remarks. The colonies of Eudendrium macquariensis so thickly invest the stems and tips of branches of the hydroid host that when first examined they seemed to be part of the host colony. Closer examination revealed white stolons of E. macquariensis running along the brown perisarc of the host. The thick aggregations on the tips of the host permits this tiny species to occupy an exceedingly crowded microhabitat. As both stolons and stems are morphologically identical it is difficult to judge at what stage the stolon becomes an erect stem.

The species is unusual in that the straggling stolon-stems are almost entirely rugose. The rugosity is usually most conspicuous in the proximal pedicel region, as usual in Eudendrium . Although the hypostome is dome-shaped rather than annular, this may be an artefact of preservation; it is, however, quite constant throughout the material. If the dome-shape is diagnostic it sets E. macquariensis somewhat apart from other known species of Eudendrium .

Figures

Figures 3A–G. A, Eudendrium deforme. A, part of colony on dead branch of primnoid gorgonian, stn 46. B, single stem. C, cluster of male gonophores with paired immature gonophores and partially resorbed tentaclesof hydranth. D, undischarged nematocyst, probably eurytele from coenosarc of stem. E–G, Eudendrium macquariensis sp. nov., stn 44. E, stems from holotype colony on Eudendrium deforme. F, undischarged nematocyst from tentacles. G, undischarged nematocyst, site unknown. Scale bar: A, 25 mm; B, 10 mm; C, 0.5 mm; E, 1 mm; F, G, 10 µm.